#pragma GCC optimize(2)
#include <iostream>
#include <sstream>
#include <string>
using namespace std;
#define endl '\n'
#define int long long

void test()
{
    int num;
    cin >> num;
    std::ostringstream ss;
    ss << num;
    string s = ss.str();
    int mid = s.length() / 2;
    while (true)
    {
        if (s.length() % 2 != 0)
        {
            cout << "no";
            break;
        }
        else if (s.substr(0, mid) == s.substr(mid))
        {

            cout << "yes";
            break;
        }
        else
            cout << "no";
        break;
    }
}

signed main()
{
    test();
    return 0;
}
